Inducible nitric oxide synthase (iNOS or NOS II) is a vital weapon in the anti-pathogen arsenal of both mammalian and invertebrate cells. In mammals, transforming growth factor-p i (TGF-J3 1) modulates the host response to pathogens such as Plasmodium, the causative agent of malaria, via a prominent role in regulation of NOS II expression. High levels of NO appear to activate latent TGF-Beta1 by nitrosylation and subsequent inactivation of the endogenous neutralizer of TGF-Beta I (the latency-associated peptide, LAP), while free heme, a potent pro-oxidant released in certain disease states, provides an additional mechanism for activation of latent TGF-Beta 1. Among invertebrates, Anopheles mosquitoes limit malaria parasite development with an inducible synthesis of NO that is localized principally to the midgut. Anopheles stephensi NOS (AsNOS) shows remarkable conservation with vertebrate NOS genes; however, little is known about how AsNOS is regulated. Our Preliminary Studies describe an A. stephensi homolog in the TGF-Beta superfamily, As60A, whose expression is induced in the midgut and correlated with parasite infection, indicating that like its vertebrate counterpart TGF-Beta 1, As60A is a marker of the host response to parasite infection. The act of bloodfeeding by Anopheles brings vertebrate and invertebrate immune components into close contact in the midgut environment. Cross talk between vertebrate cytokines and invertebrate cells has been documented under in vitro conditions. We propose to determine the physiological relevance of this cross talk by examining it under naturally occurring in vivo conditions. We hypothesize that, in the mosquito midgut, (1) mammalian TGF-Beta 1 is activated by heme released during blood digestion and induced mosquito NO and (2) that TGF-Beta I and As60A activate intersecting signaling pathways to regulate target gene expression. At a basic level, the studies proposed herein will establish whether cytokine control is a conserved feature of inducible NOS gene regulation among organisms that are separated by more than 500 million years of evolution. At a more applied level, the research proposed herein may also have implications for the control of malaria.